Magnetron tube



March 18, 1941. D. G. C. LUCK MAGNETRON TUBE Filed Sept. 28, 1938 EJHIIIMI w Z oar/=07 Zhmentol QCZM Gttorneg Mlfl Patented Mar. 18, 1941 UNITED STATES MAGNETRON TUBE David G. '0. Luck, Oaklyn, N. J assignor to Radio Corporation of America, a corporation of Delaware Application September 8 Claims.

My invention relates to magnetron tubes and moreparticularly to a method and means for coupling an output or load circuit to a thermionic tube of the magnetron type.

Thermionic tubes which are used for amplifying, generating oscillations, and the like, are provided with input and output electrodes. A grid is usually utilized as the input electrode and a plate or anode is utilized as the output elec- 10 trode. In thermionic tubes of the magnetron type, grid and anode electrodes may be used also.

In some magnetron applications end plates, or other auxiliary electrodes, are utilized either as input or output electrodes. In nearly every case,

however, the output or load circuit is connected in series with, or directly to, one of the electrodes.

By the present invention I propose an improved method of coupling an output or load circuit to a magnetron which utilizes the secondary magnetic field that is established by rotating electrons within the tube.

It is well known that the magnetic field in a magnetron causes electrons to rotate about the cathode. Thus, there is established a component of anode current which rotates about the oathode, and flows in the direction of the periphery of the cylindrical anode. This current, in accordance with well known laws, establishes a secondary magnetic field which passes through the axis of revolution. I have found that variations of this rotating current, produced either by grid control of the total electron flow or by anode voltage control of the electron velocity, produce variations in the secondary axial field. I have found also that the variations in this secondary axial field will induce a voltage in a. solenoid surrounding the tube and coaxial therewith. In accordance with my invention, therefore, I pro-' pose to utilize the voltage variations which are 40 induced in an external solenoid by this secondary field for the purpose of supplying the output current from the tube.

By adjusting the fixed magnetic field and the anode potential a condition of optimum coupling is reached. This condition is achieved when the electrons rotate the maximum number of times about the cathode in passing from the cathode to the anode. The greater the number of revolutions made by an electron, the greater the secondary magnetic field and the greater the coupling to the output. In effect, therefore, amplification is achieved by causing a strong secondary magnetic field to be built up by the repeated rotation of the electrons.

at It is an object of my invention to provide a 28, 1938, Serial No. 232,027

novel method and means for coupling a load circult to a magnetron.

It is a further object of my invention to utilize the magnetic field produced by the rotation of electrons about the cathode of a magnetron to provide a coupling to an external load circuit.

It is a still further object of my invention to couple a load circuit to a magnetron in such a manner that output currents are obtained independently of the anode circuit.

My invention will be better understood from the following description when considered in connection with the accompanying drawing. Its scope is indicated by the appended claims. Similar reference numerals refer to similar parts throughout the drawing.

Figure 1 is a perspective View of a magnetron employing an output circuit in accordance with my invention;

Figure 2 is a schematic diagram showing the device illustrated in Figure 1 and connections therefor; and

Figure 3 is a schematic drawing of an alternative method of controlling the electron flow in a magnetron.

Fig. 1 illustrates a magnetron of the single anode type. The tube consists of a cathode 5 which passes through a cylindrical anode 1, concentrically arranged about the cathode. A magnetic field substantially parallel to the axis of the cathode is produced by any suitable means, such as a horseshoe magnet 9, or the like, The cathode and anode electrodes are suitably mounted within a glass envelope II. A solenoid I3 is placed aroundthe glass envelope and is con- 1 centric with the anode electrode. If desired, a grid may be included in the tube structure, and may, for example, take the form of a helix I5 which is positioned concentrically about the cathode. No attempt has been made in the drawing to illustrate the method of mounting the various electrodes within the glass envelope, as this is well known to those skilled in the art.

The dotted line spiraling out from the cathode indicates the course of electrons due to the presence of the magnetic field. This action is well known and need not be described herein.

Fig. 2 illustrates a preferred embodiment of my invention. A magnetron constructed in the manner described with respect to the illustration ofFig. lis reproduced in Fig. 2. In addition, circuit connections are shown to illustrate how a device of this character may be utilized to amplify alternating currents.

The cathode is energized by a battery I! or the like. The negative terminal of the battery is connected to ground. A high positive potential is applied to the anode l by a battery is which is connected between the anode and ground. The input voltage, from a source which is not shown, is connected to a pair of input terminals 2i. One of the input terminals is connected to ground and the other is connected to the grid It. The output is taken from a pair of terminals 23 which are connected respectively to the two terminals of a solenoid l3 which surrounds the magnetron. A variable condenser 25, or the like, is connected across the solenoid l3, for the purpose of tuning it to resonance.

The operation of this device may well be compared to the operation of a transformer. The current flowing from anode to cathode follows a rotating path due to the repeated rotation of the electrons about the cathode. This current is comparable to the current through the primary turns of a transformer. The resultant magnetic field passes through the outer solenoid and will induce a voltage therein when the intensity of the magnetic field is varied. As pointed out.

above, the magnetic field may be varied by applying a control voltage to the grid electrode or by varying the anode potential. Other conditions being equal, the maximum output is obtained if the output circuit is resonant at the frequency of the input voltage.

Magnetrons of the usual type which employ a cylindrical anode must be slightly modified in order to permit the most efficient operation of my invention. The anode electrode is positioned between the rotating electrons and the output solenoid. To prevent the anode from acting as a short-circuited turn, it is necessary to provide an axial slit in the anode. This is illustrated by the silt 21 which appears in the drawing.

Fig. 3 is a schematic drawing to illustrate the application of a control Voltage to the anode electrode in a magnetron which does not utilize a control grid. By connecting the input voltage to terminals 2| the anode potential will be varied by the input voltage. It is seen that the input terminals 2| are now connected in series with the anode battery l9. This results in variations in the velocity of the electron fiow around the oathode. The resultant change in the secondary magnetic field induces a voltage in the output solenoid in the manner described above.

The frequency of the input voltage may vary over a wide range. Amplification will take place at audio or radio frequencies. While I have illustrated my invention by a device which has been described as an amplifier, my invention is not so limited. By properly adjusting the anode potential and the magnetic field produced by the magnet 9, ultra high frequency oscillations may be generated by the magnetron. The output circuit may then be utilized to couple the oscillations which are so generated to the load circuit. The high frequency output may be modulated in any well known manner, as by varying the grid voltage.

I claim as my invention:

1. In a device of the character described, a magnetron having cathode and anode electrodes, means for producing a steady magnetic field substantially parallel to the axis of said electrodes,

and means for energizing said cathode and anode electrodes whereby electrons emitted from said cathode follow rotating paths about said cathode and produce a secondary magnetic field parallel to the axis of said cathode, and means exclusive of said energizing means for coupling a load circuit to said secondary magnetic field.

2. In combination, a magnetron having a cathode, a grid, and a concentric cylindrical anode electrode, means for producing a magnetic field parallel to the axis of said cathode, an input circuit, an output circuit, means connecting said input circuit to said grid electrode, and an output solenoid positioned concentrically about said anode electrode and connected solely to said output circuit.

3. In a magnetron tube of the axial field type, means for creating a rotating component of anode current to produce a secondary axial magnetic field, means for varying the intensity of said secondary magnetic field, and means solely responsive to variations of said secondary magnetic field for coupling a load circuit to said magnetron.

4. In a magnetron tube of the axial field type, means for creating a rotating component of anode current to produce a secondary magnetic field, a control grid for varying said secondary field, a load circuit, and means solely responsive to the variations of said secondary field for coupling said load circuit to said magnetron.

5. The method of extracting energy from an electron discharge device which includes the steps of producing a first magnetic field perpendicular to the normal electron flow to cause said electrons to rotate about an axis substantially parallel to said field, and deriving output currents solely from the magnetic field produced by said rotating electrons.

6. The method of extracting energy from an electron discharge device which includes the steps of producing a first magnetic field perpendicular to the normal electron flow to cause said electrons to rotate about an axis substantially parallel to said first field, varying the secondary magnetic field produced by said rotating electrons, and deriving output currents solely from variations in said secondary magnetic field.

'7. The method of extracting energy from an electron discharge device which includes the steps of producing a first magnetic field perpendicular to the normal electron flow to cause said electrons to rotate about an axis substantially parallel to said first field, varying the secondary magnetic field produced by said rotating electrons in accordance with a signal, and deriving output currents solely from the variations of said secondary magnetic field.

8. In an electron discharge device having a thermionic cathode and an anode, the method of operation which includes the steps of producing a fixed magnetic field whose'lines' of force are perpendicular to the normal electron flow between said cathode and anode-electrodes tocause said electrons to follow circulatory paths before striking said anode, varying the paths of said electrons in accordance with a signal, and deriving output currents solely from the resulting variation in the secondary magnetic field pro duced by said electrons.

DAVID G. C. LUCK; 

